EDTA-enhanced phytoremediation of contaminated calcareous soils: heavy metal bioavailability,extractability, and uptake by maize and sesbania

Natural and chemically enhanced phytoextraction potentials of maize (Zea mays L.) and sesbania (Sesbania aculeata Willd.) were explored by growing them on two soils contaminated with heavy metals. The soils, Gujranwala (fine, loamy, mixed, hyperthermic Udic Haplustalf) and Pacca (fine, mixed, hyperthermic Ustollic Camborthid), were amended with varying amounts of ethylenediaminetetraacetic acid (EDTA) chelating agent, at 0, 1.25, 2.5, and 5.0 mM kg^?1 soil to enhance metal solubility. The EDTA was applied in two split applications at 46 and 60 days after sowing (DAS). The plants were harvested at 75 DAS. Addition of EDTA significantly increased the lead (Pb) and cadmium (Cd) concentrations in roots and shoots, uptake, bioconcentration factor, and phytoextraction rate over the control. Furthermore, addition of EDTA also significantly increased the soluble fractions of Pb and Cd in soil over the controls; the maximum increase of Pb and Cd was 13.1-fold and 3.1-fold, respectively, with addition of 5.0 mM EDTA kg^?1soil. Similarly, the maximum Pb and Cd root and shoot concentrations, translocation, bioconcentration, and phytoextraction efficiency were observed at 5.0 mM EDTA kg^?1 soil. The results suggest that both crops can successfully be used for phytoremediation of metal-contaminated calcareous soils.     

A phytoremediation approach using Calamagrostis ligulata and Juncus imbricatus in Andean wetlands of Peru

Emergent plant species growing in Andean natural wetlands have shown efficient phytoremediation capabilities in wetlands polluted by acid mine drainage. However, the types and amounts of heavy metals accumulated by native plant species are not well understood. In this study, we focused on determining heavy metal concentrations and bioaccumulation factors in Calamagrostis ligulata and Juncus imbricatus. Two acid wetlands located above 3,500 m a.s.l. in Ancash, Peru were assessed. Physico-chemical parameters and heavy metals concentrations in control and experimental plant samples were measured in dry and rainy seasons. Results indicated that C. ligulata and J. imbricatus aerial parts accumulated higher amounts of Fe, Zn, As and Al. Also, bioaccumulation factors revealed notable increases in As, Pb and Al, but less so in Cd, Fe and Zn. On the other hand, physico-chemical parameters of water quality (pH, temperature, dissolved oxygen, sulphides) between inflow and outflow of wetlands indicated significant differences in the presence of metals in comparison with their maximum permissible limits. Both emergent plant species showed an accumulation of heavy metals and thus the ability to recovery of water quality in wetland outflows.     

In situ phytoremediation of a soil historically contaminated by metals, hydrocarbons and polychlorobiphenyls

In the past several years, industrial and agricultural activities have led to serious environmental pollution, resulting in a large number of contaminated sites. As a result, much recent research activity has focused on the application of bioremediation technologies as an environmentally friendly and economically feasible means for decontamination of polluted soil. In this study horse manure and Populus nigra (var. italica) (HM + P treatment) have been used, at real scale level, as an approach for bioremediation of a soil historically contaminated by metals (Pb, Cr, Cd, Zn, Cu and Ni) and organic contaminants, such as polychlorobiphenyls and petroleum hydrocarbon. After one year, the HM + P phytotreatment was effective in the reclamation of the polluted soil from both organic and inorganic contaminants. A reduction of about 80% in total petroleum hydrocarbon (TPH), and 60% in polychlorobiphenyls (PCBs) and total metals was observed in the HM + P treatment. In contrast, in the horse manure (HM) treatment, used as control, a reduction of only about 30% of TPH was obtained. In order to assess both effectiveness and evolution of the remediation system to a biologically active soil ecosystem, together with the pollution parameters, the parameters describing the evolution of the soil functionality (enzymatic activities and protein SDS-PAGE pattern) were investigated. A stimulation of the metabolic soil processes (increase in dehydrogenase activity) was observed in the HM + P compared to the HM treatment. Finally, preliminary protein SDS-PAGE results have permitted the identification of proteins that have been recovered in the HM + P soil with respect to the HM; this may become a basic tool for improving the biogeochemical status of soil during the decontamination through the identification of microbial populations that are active in soil decontamination.     

Mercury proxies and mercury dynamics in a forested watershed of the US Northeast

Although many studies focus on mercury (Hg) and methylmercury (MeHg) dynamics in streams, challenges remain in identifying the relative importance of land cover and seasonality at regulating Hg and MeHg dynamics at the watershed scale. Developing robust proxies for Hg and/or MeHg determination also remains a challenge. Our study used Hg, MeHg, and dissolved organic carbon (DOC) concentration measurements and various DOC fluorescence indices to characterize Hg and DOC dynamics in a forested watershed of the US Northeast. Principal component analysis indicated that land cover/landscape position (i.e., headwater vs. wetland-influenced area vs. lake-influenced area) explained 44 % of the variance in Hg, MeHg, DOC concentrations, and DOC quality during the snow-free season, while seasonality (i.e., air temperature and discharge) explained only 21 % of the variance in the results. Furthermore, finding a good proxy for Hg that is valid across a range of landscape positions remains a challenge; however, regression analysis indicated that the fluorescence peak Humic C (excitation?=?350 nm; emission?=?max (420–480)), which corresponds to the presence of melanoidins in water, explained 21 % of the variability in MeHg concentrations across both space and time (p?=?0.001), and thus appears to be a possible proxy for MeHg determination in our study watershed. From a management perspective, land cover modifications (lake, reservoir, and wetland) are likely to play more important roles at regulating Hg, MeHg, and DOC exports at the watershed scale than long-term changes in the climate of this region.     

Mercury accumulation in caged Corbicula: rate of uptake and seasonal variation

The uptake and seasonal fluctuations of total mercury were followed in caged and uncaged Asiatic clams, Corbicula fluminea, over a 1-year period in South River, Virginia. Mercury was rapidly accumulated in clams transplanted from a nominally uncontaminated site into cages on the contaminated South River, reaching 0.99 μg g^???1 dry mass within the first month. Resident clams moved to cages had higher mercury contents after the first month (2.04 μg g^???1 dry mass) and at all subsequent times in the study. Large monthly fluctuations in mercury were noted for both resident caged and transplant caged clams with a notable peak occurring in early spring (4.31 μg g^???1 dry mass in resident caged clams). Tissue mass of caged clams steadily increased through the winter and early spring. Adjustment of mercury concentrations for tissue mass changes indicated that the changes in mercury contents were primarily due to uptake/release rather than changes in tissue mass (concentration/dilution). The present study demonstrates the utility of using caged Corbicula as mercury biomonitors and illustrates the importance of accounting for large, short-term changes of mercury content in Corbicula when designing long-term biomonitoring studies.     

Comparison of arsenic uptake ability of barnyard grass and rice species for arsenic phytoremediation

In this research, the relative performance in arsenic (As) remediation was evaluated among some barnyard grass and rice species under hydroponic conditions. To this end, four barnyard grass varieties and two rice species were selected and tested for their remediation potential of arsenic. The plants were grown for 2 weeks in As-rich solutions up to 10 mg As L^?1 to measure their tolerance to As and their uptake capabilities. Among the varieties of plants tested in all treatment types, BR-29 rice absorbed the highest amount of As in the root, while Nipponbare translocated the maximum amount of As in the shoot. Himetainubie barnyard grass produced the highest biomass, irrespective of the quantity of As in the solution. In all As-treated solutions, the maximum uptake of As was found in BR-29 followed by Choto shama and Himetainubie. In contrast, while the bioaccumulation factor was found to be the highest in Nipponbare followed by BR-29 and Himetainubie. The results suggest that both Choto shama and Himetainubie barnyard grass varieties should exhibit a great potential for As removal, while BR-29 and Nipponbare rice species are the best option for arsenic phytoremediation.     

Temporal trend of mercury in polar bears (Ursus maritimus) from Svalbard using teeth as a biomonitoring tissue

We examined the use of mercury (Hg) and nitrogen and carbon stable isotopes in teeth of polar bear (Ursus maritimus) from Svalbard as biotracers of temporal changes in Hg pollution exposure between 1964 and 2003. Teeth were regarded as a good matrix of the Hg exposure, and in total 87 teeth of polar bears were analysed. Dental Hg levels ranged from 0.6 to 72.3 ng g(-1) dry weight and increased with age during the first 10 years of life. A decreasing time trend in Hg concentrations was observed over the recent four decades while no temporal changes were found in the stable isotope ratios of nitrogen (δ(15)N) and carbon (δ(13)C). This suggests that the decrease of Hg concentrations over time was more likely due to a lower environmental Hg exposure in this region rather than a shift in the feeding habits of Svalbard polar bears.     

金汞齐富集-便携式测汞仪直接测定环境空气中的气态汞

利用金汞齐富集-便携式测汞仪对环境空气中的气态汞进行直接测定,通过对实验条件的筛选及优化,得到最佳条件。经测试,汞的质量在0～9. 20 ng之间,与对应的强度呈良好的线性关系,标准曲线的相关系数R~2=0. 997 1,RSD=8. 7%和9. 9%,方法检出限为1 ng/m~3。该方法具有简便、快捷、不使用化学试剂等优点,且对环境温度和湿度有一定的抗干扰性,适用于对环境空气气态汞的现场测定。     

Young northern pike,yellow perch and crayfish as bioindicators in a mercury contaminated watercourse

Young-of-the-year and yearling northern pike (Esox lucius), yearling yellow perch (Perca flavescens) and adult crayfish (Orconectes virilis) were collected in the mercury-contaminated Wabigoon/English/Winnipeg River System, Ontario, and analyzed for total mercury. Analysis of mercury concentrations in these organisms produced consistent geographical trends; i.e. mercury concentrations in biota downstream of Dryden > English River system > Winnipeg River system > control sites. In the Wabigoon River system the bioavailability of mercury increases with distance downstream of the historical point source. Mercury concentrations in the biota studied were highly correlated with mercury concentrations in fish species which are of sport and commercial interest. The locations where young fish obtain their bodyburdens are known typically within 100 m. The biota studied compare favourably with the criteria proposed by Phillips (1980) as prerequisites for biological indicators. The wide distribution of young pike, perch and crayfish in North America, Europe and Asia may enhance their appeal as biomonitors.The views expressed are those of the authors and do not necessarily reflect the views of the Ontario Ministry of the Environment. No endorsement should be inferred.     

Spatial variability and temporal changes in the trace metal content of soils: implications for mine restoration plan

Trace metals in soils may be inherited from the parent materials or added to the system due to anthropogenic activities. In proposed mining areas, trace metals become an integral part of the soil system. Usually, researchers undertake experiments on plant species selection (for the restoration plan) only after the termination of mining activities, i.e. without any pre-mining information about the soil-plant interactions. Though not shown in studies, it is clear that several recovery plans remain unsuccessful while carrying out restoration experiments. Therefore, we hypothesize that to restore the area effectively, it is imperative to consider the pre-mining scenario of metal levels in parent material as well as the vegetation ecology of the region. With these specifics, we examined the concentrations of trace metals in parent soils at three proposed bauxite locations in the Eastern Ghats, India, and compared them at a spatio-temporal scale. Vegetation quantification and other basic soil parameters accounted for establishing the connection between soil and plants. The study recorded significant spatial heterogeneity in trace metal concentrations and the role of vegetation on metal availability. Oxidation reduction potential (ORP), pH and cation exchange capacity (CEC) directly influenced metal content, and Cu and Ni were lithogenic in origin. It implies that for effective restoration plant species varies for each geological location.     

Monitoring of heavy metals uptake and allocation in Pinus sylvestris organs in alkalised soil

The concentration of heavy metals in soil and in Scots pine (Pinus sylvestris) organs growing on a pH gradient from 4.0 to 7.9 of soil at different distances from a cement plant was monitored. Emission for over 40 years of alkaline dust (pH 12.3-12.6) into the atmosphere in North Estonia had resulted in alkalisation and elevated concentration of total heavy metals in upper layers of the soil (0-30 cm), which was considerable even 10 years after the dust pollution stopped. Monitoring showed that the accumulation and allocation of heavy metals varied between the stem, shoots and needles and differed from the trees in the unpolluted area, depending more on the mobility of elements and the pH than element concentrations in the alkaline soil. A strong negative correlation was found between the soil pH and Mn, Zn and Cd concentrations in different tree organs. Compared to the unpolluted area, Pb was present in relatively higher concentrations in all organs but Cr, Fe and Cu in needles and shoots. The concentrations of Mn and Cd were much lower than control in all organs of trees in alkalised soil. The height increment and density of needles on shoots were predominantly in negative correlation with the pH of soil.     

Distribution of mercury and organic matter in particle-size classes in sediments contaminated by a waste water treatment plant: Vidy Bay, Lake Geneva, Switzerland

In Lake Geneva, Switzerland, the most Hg-contaminated sediments have been found in the Vidy Bay where high Hg contents largely exceeds the background levels of Lake Geneva sediments. This contamination has been attributed to the discharge of a waste water treatment plant (WWTP). Total Hg (THg) and monomethylmercury (MMHg) were determined in bulk sediment and in three different grain size fractions (i: clay and silt, ii: fine-coarse sand, iii: and very coarse sand and gravel) collected close to the outlet pipe of a WWTP in order to verify whether the standardized procedures of sediment treatment is adequate for this setting and, by extension, for similar contaminated sites. THg was homogeneously distributed in the different grain size fractions and was correlated to organic matter content (R(2) = 0.6). MMHg was homogeneously distributed in the two finer grain fractions (Φ < 0.063 mm; 0.063 mm < Φ <1 mm). The results of this study suggested that the analysis of the bulk sediment seems to be more appropriate for the assessment of the content and spatial distribution of Hg in freshwater sediments contaminated by WWTPs.     

Changes in wind erosion over a 25-year restoration chronosequence on the south edge of the Tengger Desert,China: implications for preventing desertification

Wind erosion is a primary cause of desertification as well as being a serious ecological problem in arid and semi-arid areas across the world. To determine mechanisms for restoring desertified lands, an unrestored shifting sand dune and three formerly shifting sand dunes (desertified lands) that had been enclosed and afforested for 5, 15, and 25 years were selected for evaluation on the south edge of the Tengger Desert, China. Based on sampling heights between 0.2 and 3 m, the critical threshold average wind speed was 6.5 m s^?1 at 2 m where the sand transport rate was reduced from 285.9 kg m^?2 h^?1 on the unrestored dunes to 9.1 and 1.8 kg m^?2 h^?1 on the sites afforested and enclosed for 5 and 15 years, respectively. The percentage of wind eroded area was reduced from 99.9% on the unrestored dune to 94.5, 9.0, and 0.5% on the sites afforested and enclosed for 5, 15, and 25 years, respectively. Wind erosion was effectively reduced after 15 years. Although there were different driving factors for wind erosion mitigation on the different restoration stages, an increase in the vegetation cover, surface roughness, soil shear strength, soil clay content, organic matter, and reduction in the near-surface wind speed were the primary variables associated with the restoration chronosequence. We conclude that reducing the wind speed and developing a biological crust through vegetation restoration were the critical components for restoration of desertified land.     

Native plant restoration combats environmental change: development of carbon and nitrogen sequestration capacity using small cordgrass in European salt marshes

Restoration of salt marshes is critical in the context of climate change and eutrophication of coastal waters because their vegetation and sediments may act as carbon and nitrogen sinks. Our primary objectives were to quantify carbon (C) and nitrogen (N) stocks and sequestration rates in restored marshes dominated by Spartina maritima to provide support for restoration and management strategies that may offset negative aspects of eutrophication and climate change in estuarine ecosystems. Sediment C content was between ca. 13 mg C g^?1and sediment N content was ca. 1.8 mg N g^?1. The highest C content for S. maritima was recorded in leaves and stems (ca. 420 mg C g^?1) and the lowest in roots (361?±?4 mg C g^?1). S. maritima also concentrated more N in its leaves (31?±?1 mg N g^?1) than in other organs. C stock in the restored marshes was 29.6 t C ha^?1; ca. 16 % was stored in S. maritima tissues. N stock was 3.6 t N ha^?1, with 8.3 % stored in S. maritima. Our results showed that the S. maritima restored marshes, 2.5 years after planting, were sequestering atmospheric C and, therefore, provide some mitigation for global warming. Stands are also capturing nitrogen and reducing eutrophication. The concentrations of C and N contents in sediments, and cordgrass relative cover of 62 %, and low below-ground biomass (BGB) suggest restored marshes can sequester more C and N. S. maritima plantations in low marshes replace bare sediments and invasive populations of exotic Spartina densiflora and increase the C and N sequestration capacity of the marsh by increasing biomass production and accumulation.     

Uncertainty assessment of mapping mercury contaminated soils of a rapidly industrializing city in the Yangtze River Delta of China using sequential indicator co-simulation

Accurate characterization of heavy-metal contaminated areas and quantification of the uncertainties inherent in spatial prediction are crucial for risk assessment, soil remediation, and effective management recommendations. Topsoil samples (0–15 cm) (n = 547) were collected from the Zhangjiagang suburbs of China. The sequential indicator co-simulation (SIcS) method was applied for incorporating the soft data derived from soil organic matter (SOM) to simulate Hg concentrations, map Hg contaminated areas, and evaluate the associated uncertainties. High variability of Hg concentrations was observed in the study area. Total Hg concentrations varied from 0.004 to 1.510 mg kg⁻¹ and the coefficient of variation (CV) accounts for 70%. Distribution patterns of Hg were identified as higher Hg concentrations occurred mainly at the southern part of the study area and relatively lower concentrations were found in north. The Hg contaminated areas, identified using the Chinese Environmental Quality Standard for Soils critical values through SIcS, were limited and distributed in the south where the SOM concentration is high, soil pH is low, and paddy soils are the dominant soil types. The spatial correlations between Hg and SOM can be preserved by co-simulation and the realizations generated by SIcS represent the possible spatial patterns of Hg concentrations without a smoothing effect. Once the Hg concentration critical limit is given, SIcS can be used to map Hg contaminated areas and quantitatively assess the uncertainties inherent in the spatial prediction by setting a given critical probability and calculating the joint probability of the obtained areas.     

Tidally driven N, P, Fe and Mn exchanges in salt marsh sediments of Tagus estuary (SW Europe)

Short-sediment cores and flooding water were collected at 0, 5, 15, 25 and 50?min of tidal inundation in the two sites colonised by pure stands of Spartina maritima (low marsh) and Sarcocornia fruticosa (high marsh) from the Rosário salt marsh (Tagus estuary, SW Europe). Concentrations of NH (4) (+) , NO (3) (-) +?NO (2) (-) and HPO (4) (2-) , Fe and Mn were measured in tidal flooding water and pore water. Flooding water is enriched in nutrients, particularly ammonium due to local discharge of untreated urban effluents. Nevertheless, NH (4) (+) and NO (3) (-) +?NO (2) (-) concentrations in flooding waters at t?=?5?min (NH (4) (+) =?246?±?7?μM, NO (3) (-) +?NO (2) (-) =?138?±?1?μM for S. fruticosa and NH (4) (+) =?256?±?8?μM, NO (3) (-) +?NO (2) (-) =?138?±?1?μM for S. maritima) rose sharply at both vegetated sites. An increase was also registered for HPO (4) (2-) and total dissolved Fe although the subsequent decrease was smoother. Advective transport induced by the two daily pulses of inundation is several orders of magnitude higher than the diffusive fluxes during submerged periods. In addition, solutes are exported from the sediment with the inundation and imported in submerged periods. The exported amount of inorganic nitrogen during tidal inundation (export of 3,200?μmol?N?m(-2)?day(-1)to the water column), is not counterbalanced by the sink of -290?μmol?N?m(-2)?day(-1) occurred during the submerged period.